/*
 * parse.c — line-oriented parser for the asm subset emitted by w6c.
 *
 * Grammar:
 *   line := blank | comment | label | text | instr
 *   blank := /^\s*$/
 *   comment := /^\s*\/\/.*$/
 *   label := /^IDENT:$/
 *   text  := TEXT name,$framesize
 *   instr := \tMNEM\t[OP1[, OP2]]
 *   OP    := $NUM | REG | NUM(REG) | (REG) | name(SB) | label
 *
 * Identifiers may include '.' and '_'. Whitespace inside operands
 * (between '$' and a number, etc.) is rejected for sanity.
 */
#include "a.h"
#include <ctype.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

extern int  a_isidstart(int);
extern int  a_isidcont(int);
extern i64  a_parsenum(const char *, char **);

void
a_init(Asm *a, const char *file, const char *src, u64 len)
{
	memset(a, 0, sizeof *a);
	a->file = file;
	a->src = src;
	a->srclen = len;
	a->line = 1;
}

static void
err(Asm *a, const char *msg)
{
	fprintf(stderr, "w6a: %s:%d: %s\n", a->file, a->line, msg);
	a->errs++;
}

Asym *
a_intern(Asm *a, const char *name)
{
	for (Asym *s = a->syms; s; s = s->next)
		if (strcmp(s->name, name) == 0) return s;
	Asym *s = calloc(1, sizeof *s);
	s->name = strdup(name);
	s->next = a->syms;
	a->syms = s;
	return s;
}

/* ------------------------------------------------------------------ */
/* line iterator: returns the next line as a NUL-terminated buffer in
 *   line/llen pointers, advances pos. Returns 0 on EOF.
 */
static int
nextline(Asm *a, char **line, size_t *llen, char *buf, size_t bufsz)
{
	if (a->pos >= a->srclen) return 0;
	size_t n = 0;
	while (a->pos < a->srclen && a->src[a->pos] != '\n' && n + 1 < bufsz)
		buf[n++] = a->src[a->pos++];
	buf[n] = '\0';
	if (a->pos < a->srclen && a->src[a->pos] == '\n') a->pos++;
	*line = buf;
	*llen = n;
	return 1;
}

/* skip leading whitespace */
static const char *
skipws(const char *p)
{
	while (*p == ' ' || *p == '\t') p++;
	return p;
}

static int
opcode_lookup(const char *m)
{
	struct { const char *m; int op; } tab[] = {
		{ "MOVQ", A_MOVQ }, { "MOVL", A_MOVL },
		{ "MOVW", A_MOVW }, { "MOVB", A_MOVB },
		{ "MOVZBQ", A_MOVZBQ }, { "MOVZWQ", A_MOVZWQ },
		{ "MOVSXD", A_MOVSXD }, { "MOVSWQ", A_MOVSWQ },
		{ "MOVSBQ", A_MOVSBQ },
		{ "MOVSD", A_MOVSD },
		{ "ADDSD", A_ADDSD },{ "SUBSD", A_SUBSD },
		{ "MULSD", A_MULSD },{ "DIVSD", A_DIVSD },
		{ "UCOMISD", A_UCOMISD },
		{ "CVTTSD2SI", A_CVTTSD2SI },
		{ "CVTSI2SD",  A_CVTSI2SD },
		{ "MOVSS", A_MOVSS },
		{ "ADDSS", A_ADDSS },{ "SUBSS", A_SUBSS },
		{ "MULSS", A_MULSS },{ "DIVSS", A_DIVSS },
		{ "UCOMISS", A_UCOMISS },
		{ "CVTTSS2SI", A_CVTTSS2SI },
		{ "CVTSI2SS",  A_CVTSI2SS },
		{ "CVTSD2SS",  A_CVTSD2SS },
		{ "CVTSS2SD",  A_CVTSS2SD },
		{ "ADDQ", A_ADDQ }, { "SUBQ", A_SUBQ },
		{ "IMULQ",A_IMULQ},{ "IDIVQ",A_IDIVQ},
		{ "DIVQ", A_DIVQ },{ "CQO",  A_CQO  },
		{ "NEGQ", A_NEGQ },{ "NOTQ", A_NOTQ },
		{ "ANDQ", A_ANDQ },{ "ORQ",  A_ORQ  },
		{ "XORQ", A_XORQ },
		{ "SHLQ", A_SHLQ },{ "SHRQ", A_SHRQ },
		{ "CMPQ", A_CMPQ },
		{ "PUSHQ",A_PUSHQ},{ "POPQ", A_POPQ },
		{ "LEAQ", A_LEAQ },
		{ "CALL", A_CALL },{ "RET",  A_RET  },
		{ "JMP",  A_JMP  },
		{ "JE",   A_JE   },{ "JNE",  A_JNE  },
		{ "JL",   A_JL   },{ "JLE",  A_JLE  },
		{ "JG",   A_JG   },{ "JGE",  A_JGE  },
		{ "JB",   A_JB   },{ "JBE",  A_JBE  },
		{ "JA",   A_JA   },{ "JAE",  A_JAE  },
		{ "JZ",   A_JZ   },{ "JNZ",  A_JNZ  },
		{ "SYSCALL", A_SYSCALL },
		{ "TEXT", A_TEXT },
		{ "DATA", A_DATA },
		{ "DATAW", A_DATAW },
		{ "DATAR", A_DATAR },
		{ NULL, 0 }
	};
	for (int i = 0; tab[i].m; i++)
		if (strcmp(tab[i].m, m) == 0) return tab[i].op;
	return 0;
}

static int
reg_lookup(const char *r)
{
	struct { const char *m; int reg; } tab[] = {
		{ "AX", D_AX }, { "BX", D_BX }, { "CX", D_CX }, { "DX", D_DX },
		{ "SP", D_SP }, { "BP", D_BP }, { "SI", D_SI }, { "DI", D_DI },
		{ "R8", D_R8 }, { "R9", D_R9 }, { "R10", D_R10 },
		{ "R11", D_R11 }, { "R12", D_R12 }, { "R13", D_R13 },
		{ "R14", D_R14 }, { "R15", D_R15 },
		{ "X0", D_X0 }, { "X1", D_X1 }, { "X2", D_X2 }, { "X3", D_X3 },
		{ "X4", D_X4 }, { "X5", D_X5 }, { "X6", D_X6 }, { "X7", D_X7 },
		{ "X8", D_X8 }, { "X9", D_X9 }, { "X10", D_X10 },
		{ "X11", D_X11 }, { "X12", D_X12 }, { "X13", D_X13 },
		{ "X14", D_X14 }, { "X15", D_X15 },
		{ "SB", D_PSB }, { "FP", D_PFP },
		{ NULL, 0 }
	};
	for (int i = 0; tab[i].m; i++)
		if (strcmp(tab[i].m, r) == 0) return tab[i].reg;
	return 0;
}

static int
parse_operand(Asm *a, const char *s, Aoperand *out)
{
	while (*s == ' ' || *s == '\t') s++;
	if (*s == '\0') { out->type = D_NONE; return 0; }

	if (*s == '$') {
		s++;
		char *end;
		out->type = D_CONST;
		out->offset = a_parsenum(s, &end);
		return 0;
	}

	/* (REG) form */
	if (*s == '(') {
		s++;
		char rbuf[8] = {0};
		int n = 0;
		while (*s && *s != ')' && n < 7) rbuf[n++] = *s++;
		if (*s != ')') { err(a, "missing ')' in indirect"); return -1; }
		int r = reg_lookup(rbuf);
		if (r == 0) { err(a, "bad register in indirect"); return -1; }
		out->type = D_INDIR;
		out->reg = r;
		out->offset = 0;
		return 0;
	}

	/* number(REG) form, or label form, or REG */
	const char *p = s;
	int sign = 1;
	if (*p == '-') { sign = -1; p++; }
	if (isdigit((unsigned char)*p)) {
		char *end;
		i64 off = a_parsenum(s, &end);
		if (*end == '(') {
			char rbuf[8] = {0};
			int n = 0;
			end++;
			while (*end && *end != ')' && n < 7) rbuf[n++] = *end++;
			if (*end != ')') { err(a, "missing ')'"); return -1; }
			int r = reg_lookup(rbuf);
			if (r == 0) { err(a, "bad register"); return -1; }
			out->type = D_INDIR;
			out->reg = r;
			out->offset = off;
			return 0;
		}
		out->type = D_CONST;
		out->offset = off * sign;
		return 0;
	}

	/* IDENT — register or symbol-or-label */
	if (a_isidstart((unsigned char)*s)) {
		char buf[64] = {0};
		int n = 0;
		while (a_isidcont((unsigned char)*s) && n < 63) buf[n++] = *s++;
		buf[n] = 0;

		/* Optional `+disp` between the ident and `(SB)`. Used by
		 * DATAR to address bytes inside an existing .data slot
		 * (e.g. `DATAR s+8(SB),...`). */
		i64 sym_disp = 0;
		if (*s == '+') {
			s++;
			char *end;
			sym_disp = a_parsenum(s, &end);
			s = end;
		}

		/* ID(SB) means external symbol */
		if (*s == '(') {
			char rbuf[8] = {0};
			int rn = 0;
			s++;
			while (*s && *s != ')' && rn < 7) rbuf[rn++] = *s++;
			if (*s != ')') { err(a, "missing ')'"); return -1; }
			s++;
			int r = reg_lookup(rbuf);
			if (r == D_PSB) {
				out->type = D_EXTERN;
				out->sym = strdup(buf);
				out->offset = sym_disp;
				return 0;
			}
			out->type = D_INDIR;
			out->reg = r;
			out->offset = 0;
			/* unusual case: name(REG) with named offset; not used */
			return 0;
		}

		int r = reg_lookup(buf);
		if (r != 0) {
			out->type = r;
			return 0;
		}
		/* otherwise it's a branch target */
		out->type = D_BRANCH;
		out->sym = strdup(buf);
		return 0;
	}

	err(a, "unrecognised operand");
	return -1;
}

int
a_parse(Asm *a)
{
	/* Big enough for a DATAW emitting a [256]u32 table (1024 bytes
	 * → ~4100 chars of `\xNN` escapes plus directive boilerplate).
	 * Selfhost w6a allocates per-line; this is the cstage equivalent. */
	static char buf[32768];
	char *line;
	size_t len;
	const char *pending_label = NULL;

	while (nextline(a, &line, &len, buf, sizeof buf)) {
		const char *p = skipws(line);
		if (*p == '\0' || (*p == '/' && p[1] == '/')) {
			a->line++;
			continue;
		}

		/* label? */
		if (a_isidstart((unsigned char)*p) && line[0] != '\t') {
			const char *q = p;
			while (a_isidcont((unsigned char)*q)) q++;
			if (*q == ':') {
				size_t nl = q - p;
				char *name = malloc(nl + 1);
				memcpy(name, p, nl);
				name[nl] = '\0';
				/* If a label is already pending we'd lose it
				 * by overwriting; flush it onto a NOP prog so
				 * each label still pins to a real address. */
				if (pending_label) {
					Aprog *prg = calloc(1, sizeof *prg);
					prg->as = A_NOP;
					prg->label = pending_label;
					prg->line = a->line;
					if (a->head == NULL) a->head = prg;
					else a->tail->link = prg;
					a->tail = prg;
				}
				pending_label = name;
				a->line++;
				continue;
			}
		}

		/* TEXT or instruction */
		const char *m = p;
		char mnem[16] = {0};
		int n = 0;
		while (*m && *m != ' ' && *m != '\t' && n < 15) mnem[n++] = *m++;
		mnem[n] = '\0';

		int op = opcode_lookup(mnem);
		if (op == 0) {
			err(a, "unknown opcode");
			a->line++;
			continue;
		}

		Aprog *prg = calloc(1, sizeof *prg);
		prg->as = op;
		prg->line = a->line;
		prg->label = pending_label;
		pending_label = NULL;

		while (*m == ' ' || *m == '\t') m++;
		const char *rest = m;

		if (op == A_TEXT) {
			/* TEXT name,$framesize */
			char nbuf[64] = {0};
			int nn = 0;
			while (*m && *m != ',' && nn < 63) nbuf[nn++] = *m++;
			prg->to.type = D_EXTERN;
			prg->to.sym = strdup(nbuf);
			if (*m == ',') {
				m++;
				while (*m == ' ' || *m == '$') m++;
				prg->from.type = D_CONST;
				prg->from.offset = a_parsenum(m, NULL);
			}
		} else if (op == A_DATA || op == A_DATAW) {
			/* DATA  name(SB),"escaped bytes" — read-only in .text
			 * DATAW name(SB),"escaped bytes" — writable in .data */
			char nbuf[128] = {0};
			int nn = 0;
			while (*m && *m != '(' && nn < 127) nbuf[nn++] = *m++;
			prg->to.type = D_EXTERN;
			prg->to.sym = strdup(nbuf);
			if (*m == '(') {
				while (*m && *m != ')') m++;
				if (*m == ')') m++;
			}
			while (*m == ' ' || *m == ',' || *m == '\t') m++;
			if (*m != '"') {
				err(a, "DATA expects \"...\"");
				prg->bytes = NULL;
				prg->nbytes = 0;
			} else {
				m++;
				/* parse escapes into a fresh buffer */
				size_t cap = 32, len = 0;
				u8 *buf = malloc(cap);
				while (*m && *m != '"') {
					int c = (unsigned char)*m++;
					if (c == '\\' && *m) {
						int e = (unsigned char)*m++;
						switch (e) {
						case 'n': c = '\n'; break;
						case 't': c = '\t'; break;
						case 'r': c = '\r'; break;
						case '\\': c = '\\'; break;
						case '"': c = '"'; break;
						case '0': c = 0; break;
						case 'x': {
							int hi = (unsigned char)*m++;
							int lo = (unsigned char)*m++;
							int h = (hi<='9'?hi-'0':(hi|0x20)-'a'+10);
							int l = (lo<='9'?lo-'0':(lo|0x20)-'a'+10);
							c = (h << 4) | l;
							break;
						}
						default: c = e; break;
						}
					}
					if (len + 1 > cap) {
						cap *= 2;
						buf = realloc(buf, cap);
					}
					buf[len++] = (u8)c;
				}
				prg->bytes = buf;
				prg->nbytes = len;
			}
		} else {
			/* split rest at top-level comma */
			const char *comma = NULL;
			for (const char *q = rest; *q; q++)
				if (*q == ',' && comma == NULL) comma = q;
			if (comma) {
				char op1[256], op2[256];
				size_t l1 = comma - rest;
				if (l1 >= sizeof op1) l1 = sizeof op1 - 1;
				memcpy(op1, rest, l1); op1[l1] = '\0';
				size_t l2 = strlen(comma + 1);
				if (l2 >= sizeof op2) l2 = sizeof op2 - 1;
				memcpy(op2, comma + 1, l2); op2[l2] = '\0';
				parse_operand(a, op1, &prg->from);
				parse_operand(a, op2, &prg->to);
			} else if (*rest) {
				parse_operand(a, rest, &prg->to);
			}
		}

		if (a->head == NULL) a->head = prg;
		else a->tail->link = prg;
		a->tail = prg;
		a->line++;
	}
	return a->errs;
}